1. Field of the Invention
The present application relates to an aspiration system for a medical aspiration system.
2. Prior Art
The lens of a human eye may develop a cataracteous condition which affects a patients vision. Cataracteous lenses are sometimes removed and replaced in a procedure commonly referred to as phacoemulsification. Phaco procedures are typically performed with an ultrasonically driven hand piece which is used to break the lens. The broken lens is removed through an aspiration line that is coupled to the hand piece.
The hand piece has a tip that is inserted through an incision in the cornea. The hand piece typically contains a number of ultrasonic transducers that convert electrical power into a mechanical oscillating movement of the tip. The distal end of the tip has an opening that is in fluid communication with the aspiration line. The distal end of the tip also has a sleeve which has an opening in fluid communication with an irrigation line. The irrigation line is typically connected to a bottle that can provide irrigation fluid to the surgical site.
The oscillating movement of the tip breaks the lens into small pieces. The lens pieces and irrigation fluid are drawn into the aspiration line through the opening of the tip. When performing a phaco procedure it is essential to maintain a positive pressure within the anterior chamber of the eye. A negative pressure may cause the cornea to collapse. To maintain a positive chamber pressure the system is configured to provide a flow rate through the irrigation tube that is greater than the flow rate through the aspiration tube.
It has been found that the aspiration system may become occluded, especially at the hand piece tip, during a procedure. The occlusion will increase the vacuum pressure within the aspiration line. The increase in pressure may pull the occluded particle through the aspiration system. The surgeon may also break the occluding piece of lens into smaller pieces. When the occlusion is cleared the anterior chamber may be instantaneously exposed to a high vacuum pressure. The vacuum pressure may cause the cornea to collapse.
Occlusions can also be cleared by depressing a reflux bulb attached to the system. The reflux bulb creates a surge of fluid through the system that creates a fluidic force that can dislodge the occlusion.
U.S. Pat. No. 6,478,781 issued to Urich et al. discloses a coiled tube that can be used to minimize pressure surges in an aspiration system. The tube has a length of at least 8 feet and a number of coils that create a fluidic resistance which minimizes vacuum surges. The recited inner diameter of the tube ranges from 0.06 to 0.1 inches, which is industry standard. Although effective, the coiled approach can only account for a limited reduction of the vacuum surge. Additionally, the coil is susceptible to occlusions within the coiled tube.
U.S. Pat. No. 6,599,271 issued to Easley and assigned to Syntec, Inc. discloses an aspiration system that has a flow restrictor and an in-line filter. Likewise, STAAR Surgical of Monrovia, Calif. sells an in-line filter under the name CRUISE CONTROL that contains a flow restrictor. The flow restrictors limit the vacuum surges within the aspiration system.
Conventional phaco procedures are typically performed using a vacuum pressure of about 250 mmHg. There is a desire to increase the vacuum pressure to assist in aspirating larger pieces of the lens. Aspirating larger pieces lowers the amount of ultrasonic work that must be performed on the eye. Lowering the ultrasonic work is desirable because ultrasound can irritate the eye. Consequently, there is a desire to create vacuums up to 500 mmHg to improve aspiration and reduce the amount of ultrasound delivered to the cornea.
In order to achieve effective flow and vacuum surge clamping with flow restrictors, the inner diameter of the restriction must be very small, usually smaller than 0.0010 inch. If lens particles are larger than 0.0010 inch, residues of ultrasonic emulsification or viscous fluids used in surgery escape the filter, and the entire aspiration line can become occluded. Consequently, the filter volume must be large enough to hold all the extracted lens and viscous fluids. The extra amount of fluid added to the aspiration line by the filter increases the compliance of the system which makes the aspiration sluggish. In addition, there is an increased volume of dissolved air which increases the vacuum surge.
Vacuum pressures of 400 mmHg or greater will create turbulent flow in systems that have flow restrictors. The turbulent flow can create air bubbles that become trapped in the filter. When an occlusion occurs the bubbles may create a fluidic spring that generates surges in the system. Additionally, the internal restrictors create a choke point that limits the amount of fluid force created during a reflux cycle. This limits the effectiveness of depressing the reflux bulb to clear an occlusion. It would be desirable to provide a low cost aspiration system that can effectively minimize fluid surges even at relatively high vacuum pressures, and not create a choke point or create turbulent bubbles.